Somebody That I Used to Know
by MollyCarpenter
Summary: Waking up to Cas pounding to be let in is bad enough. Discovering that it's the Cas from the post-apocalyptic future is worse. But then there's not being able to get hold of the present-day Castiel, and things start to go downhill fast...
1. Late Night Visitors

It was four in the morning when Dean startled awake.

For a moment he wasn't sure what had woken him; for once it hadn't been a nightmare, because Sam was stirring too. Then the rapping on the door was repeated, and they both turned to look.

They slid out of bed simultaneously, Dean with the Colt in his hand—he'd taken to sleeping with it under his pillow—and Sam opening the bedside table's drawer for Ruby's knife. As Dean's feet hit the floor, the person knocking spoke.

"Dean, Dean are you in there? Please be in there," and they both froze for half a second because it was _Cas_, only he sounded like he was about to keel over. Dean waved Sam over to stand behind the door and traded him the Colt for the knife. The doorknob rattled. "Dean? It's me, please."

"Cas," Dean said, pitching his voice just loud enough to be heard through the door. "Why aren't you coming in?" It was a damn weird time for Cas to be working out that you couldn't just pop into someone's room.

Cas's reply was confused, and wearily amused in a way that made Dean's stomach twist with an uncomfortable familiarity he couldn't quite pin down. "The door's locked?" Cas said. "Unless you want me to break it. I think I can break it."

Dean threw Sam a glance and saw equal puzzlement on his brother's face—Cas could punch people through brick walls; a motel door shouldn't faze him. They held a brief consultation in their expressions and finally Sam shrugged. Dean agreed with him. "OK, just a sec, I'm opening it," Dean said. He turned the latch and undid the chain, and eased the door open a few inches.

The light over the door cast uneasy shadows on Cas's face, but several things were clear: he was slumped against the doorjamb like he was using it to hold himself up, he was not wearing his suit or coat, and his usual five-o'clock shadow had transmuted itself into most of a week's worth of beard in the roughly ten hours since Dean had seen him last, off on another God-finding expedition. His eyes were fever-bright, pupils shrunk to pinpricks, and when he finally focused on Dean his mouth fell open in obvious shock. "Dean," he said finally, barely more than a whisper. "Oh Father help me, Dean, it's you."

"Uh…yeah," Dean said, and then realized what he was looking at. _Sonuvabitch_, he thought, in that part of his brain that was always calm. "Come on, Cas, you can't stand out there, it's cold out," he said, marveling at the evenness of his own voice. It was chilly, anyway, and Cas was wearing sandals, light cotton pants and, if Dean was not mistaken, that very same blue shirt. Cas nodded as if Dean had said something profound and said clearly, "You don't need to deal with me getting sick on top of everything else. But I don't get sick, Dean, you know that, I don't…get…" He trailed off, and Dean had to drop the knife to catch him as he folded at the knees.

He dragged Cas over the salt line and the few steps to his bed, letting the man fall in a more-or-less comfortable looking sprawl. Behind him Sam closed and locked the door and flicked on the overhead light. As he turned, his eyebrows practically crawling into his hairline, Sam got his first good look at Cas and froze.

"What the hell?" Sam said.

Dean sighed. "When Zach sent me to the zombie apocalypse," he said. He couldn't seem to tear his eyes away from Cas, who was twitching in his sleep, but he caught Sam's nod out of the corner of his eye. "This is…Cas from then." Sam let out a heavy breath. "He's human, Sam. Not to mention on…basically any drug he could find, as far as I could tell, and the me from the future sent him into a trap to die."

"Human," Sam said, which Dean supposed was really the central point there, not Cas's junkiedom or his own future incredible douchebaggery. "How?"

"He said it happened when the other angels left," Dean said. Sam made a small, surprised noise, but then his face changed to an expression Dean knew far too well; that expression meant Sam was about to say something he didn't think Dean was going to like.

"Dean…are you sure this, well, _is_ Cas?" Sam asked carefully.

"No," Dean said grimly, though he couldn't help but grin a little at Sam's relief. "I think we better run the drill on him. But hey, at least he crossed the salt."

"Yeah," Sam said, and turned to his bag for the silver knife.


	2. Catching On and Catching Up

Cas passed all the tests; holy water didn't smoke on his skin and neither the silver nor iron blade produced anything more than normal scratches. That done, Dean pulled out his cell and hit Cas's...well, OK, _Castiel's_ number in the speed dial.

It dropped to voicemail immediately and Dean waited, tapping his fingers on his thigh, while the recorded voice told him that number was unavailable and he should leave a message. "Cas, uh, we've got, we've got something you should take a look at. It's, damn it. When Zachariah sent me to the future...it's you, the you from the future, he's here and we need to figure out why. We're still in the same motel. Come as soon as you get this, OK? And you should set your voicemail up right."

"No Cas?" Sam asked. He tucked the knives back into his bag and then went to flip his laptop open.

"He must be somewhere out of range of the towers," Dean agreed, sitting down on Sam's bed. "Who the hell knows where he looks for God anyway?"

"At least he didn't take you seriously when you told him to check prisons." Sam paused. "Did he?"

"Not once I explained the joke," Dean said. It maybe should have occurred to him after the flatbread thing that telling Cas how a lot of guys found God behind bars was likely to lead to a rash of prison guards tripping over an angel in a trenchcoat; fortunately he'd managed to catch him before he went and started actually searching prisons. He'd been kind of pissy when Dean told him it wasn't really a lead, too.

Meanwhile they had to decide what to do with this Cas, who looked like he'd lost every bit of what little fat Jimmy Novak, that poor bastard, had possessed, and who Dean suspected wasn't asleep so much as deeply, profoundly out of his mind on whatever he'd taken. This Cas was all stringy muscle and sharp bone, and Dean hated to look at him at exactly the same time that he could hardly look away.

He had no idea how Cas had come to be here, and he was sincerely not sure he cared. Sure, living in motels could suck, but at least motels had, like, 24-hour electricity and hot water. (Dean had taken a shower at Camp Chitaqua; it had been lukewarm—for the first thirty seconds—and the showerhouse had smelled like mold.) And they could get Cas some decent food once he woke up, and maybe get him off whatever pills he was taking.

"Maybe we should take him to Bobby's," Sam said, breaking into Dean's train of thought. "At the very least we'd be able to do some better research into what might've done this."

"Not much that could've," Dean said. The list was...really short, and mostly had angels on it. In fact Dean couldn't think of _anything_ but angels that could've done this, but he also had no idea why one would. There weren't even any angels left in 2014, and none of the present-day feathery dickheads would have reason to do Cas any favors. Except Anna, maybe, but she'd have stuck around to explain, right? It wasn't like Gabriel had shown any particular affection for his kid brother.

"Yeah," Sam said, and Dean could tell from his tone of voice that he'd done much the same calculations. "I can't think of anything except..."

"Yeah," Dean said. Morose silence fell. "OK," he continued after a minute. "Bobby's it is, but we should probably let him sleep off whatever this is. Don't want him waking up in the middle of the interstate."

Sam made a noise of agreement and turned back to his computer, shooting occasional quick glances at Cas around the screen that Dean recognized as queasy fascination, a sentiment he could sympathize with. Dean got resolutely to his feet and pulled out the gun bag to do a little cleaning.

He had Sam's Taurus in pieces all around him when Cas choked on nothing, rolled onto his side, and started retching. Dean managed not to lose any gun parts in his haste to get to Cas's side, which slowed him enough that Sam snagged the wastebasket first. Between them they got his head over the edge of the bed right before he vomited in earnest; there hadn't been much in his stomach, apparently, but the dry heaves went on for minutes. Dean winced every time, because as far as he was concerned there wasn't much your own body could do to you that was nastier than trying to puke when there was nothing to bring up. He sat next to Cas through it, and didn't object when Cas's hand wrapped around his wrist and squeezed, harder than a scrawny guy like him should've been able to manage. Dean kind of figured that the amount of screwing over his future self had done to Cas deserved a little payback, so he let the bones of his wrist grind without complaint.

Finally Cas's death-grip eased and the heaves died down. He panted for a few seconds. When he spoke it was without opening his eyes, but in the same casually sarcastic way that Dean remembered far too well. "OK. Next time I'm gonna listen when you tell me not to take the pink mystery pills."

"Good call," Dean said. Cas twitched and made a convulsive movement that got him mostly back on the bed, settling onto his back before he opened his eyes. They were bloodshot, but at least his pupils were the right size. "Damn," Cas said in a tone of quiet wonder. "It wasn't a hallucination."

Dean had absolutely no idea what to say to that. Cas just stared at him for long enough that it began to be uncomfortable, until Sam, who'd been hovering in the background (and probably wringing his hands or something), shifted and cleared his throat.

Cas startled visibly and his gaze snapped away from Dean. He stared at Sam for a second, perfectly still, and then said, "No," in a flat, even voice that was somehow worse than any terrified gasp would have been. Sam's eyes widened and he looked at Dean.

"You didn't tell me I said yes," Sam said. Dean winced. He'd been hoping not to mention that detail, but of course Sam had figured it out. He gave his brother a helpless shrug that promised apologies in the future and turned to Cas. "He's not," he said firmly. "Not here, not _now_. He's still Sam here." Cas continued to watch Sam like a mouse watching a cat, and it made Dean feel sick. He leaned to block Cas's line of sight, staring into Cas's eyes. "Cas," he said, trying to be firm without snapping. "Cas. That's _Sam_."

Cas opened his mouth and appeared to stall out on what to say. Dean sighed. "I swear to you, OK? It's 2009, and that is Sam."

"2009?" Cas repeated. Dean nodded. "How?"

"Your guess is as good as ours," Dean said. "Maybe better."

Cas appeared to think it over for a second, and Dean found himself holding his breath. "I guess there's nothing I can do about it if you're lying," Cas said at last. "So OK." He grinned, that wide, empty grin that set Dean's teeth on edge. "But you know me…you know what _happened_ to me." Dean nodded. Cas made an expansive gesture and shoved himself up on the bed till he was leaning on the wall. "This I have got to hear."

Dean thought about it, trying to sum it up, and gave it up as a lost cause. "About two and a half months ago, I was in Kansas City," he said. "Zachariah had spies out, and one of 'em dropped a dime on me. I went to bed and when I woke up, I was in 2014. First thing I knew about it was a little girl, tried to gut me with a piece of broken window. Then a whole pack of them, chased me, they'd have gotten me too if the Army hadn't shown up." Cas looked fascinated. So did Sam, for that matter; Dean's summary to him had been way more along the lines of _It was bad, and it was bad because we stayed apart_ than anything detailed. "Gave them all the slip, got out of the city, lifted a car—I had to siphon three other cars to get enough gas to get to Bobby's. On the way Zach showed up and got all intimidating about how I have to say yes to Michael and then screwed off like a gigantic douche. When I got to Bobby's, all I found was his wheelchair, with bullet holes in the back." Cas winced; it was subtle, but Dean was used to looking for tiny changes on that face. He decided he was going to get the story of what exactly had happened to Bobby, damn it. "He had a hideyhole, though, and there was a picture in it—you and him and a couple other guys outside the gate. Siphoned some more gas, got to the camp in the middle of the night."

"I remember that picture," Cas said thoughtfully. "You thought it was dumb."

"Bobby's always tryin' to take pictures of things," Dean said shortly, remembering watching Jo's face curl up and burn. "When I got there…Jesus." He looked at Sam and said, "My baby was junked. Worse than after the truck hit her." Sam looked faintly appalled, Dean was gratified to note. "And then the other me snuck up on me and knocked me out. I came to in his cabin handcuffed to the ladder."

"Kinky," Cas said. Both of them blinked at him for a second. "What?"

"Kinky?" Sam repeated. He sounded like he wasn't sure he'd heard correctly. Cas smirked.

"Come on," he said. "Two versions of Dean, one of 'em in handcuffs? Excuse me while I..._appreciate _that image for a second." Sam screwed up his face in a way Dean would have found hilarious under most other circumstances. As it was he sorta wanted to make the same face, and also that answered one of his questions about his future relationship with Cas—a question he'd been carefully not examining too closely.

"Anyway," Dean continued, a little louder than he'd meant to. "Future me left me alone to go on a mission, and I managed to pick the cuffs. I met Risa, and Chuck, and you. When future me got back, he had the Colt."

That went through Cas like an electric charge; his careless sprawl didn't change, but Dean could see him tensing. "So we had a meeting, and future me came up with the stupidest frickin' plan I have ever heard. It was basically, go where Lucifer is, send everyone but him and me in the front as Polish mine detectors, and let everyone else get killed so he could take his shot at the Devil." Dean paused, feeling Cas's eyes heavy on him, with no disbelief whatsoever, and there was another question answered. Cas had _known_. He'd known future-Dean was gonna let him get killed. Dean swallowed. "On the way there you told me about the angels leaving." Cas looked mildly surprised at that, which Dean didn't really get. "So we got there, and dude, I swear—I tried to warn you, but that bastard sucker-punched me and by the time I got my act together you were already in the building." Dean couldn't look at Cas, didn't want to look at Sam, so he stared at the wall instead. "I don't know if he got his shot, not that it would've mattered. By the time I found him, Lucifer was breaking his neck." Dean almost managed to be amused by how identical Sam and Cas's responses were to that—they both winced, and looked down, and came back up looking murderous. "So Lucifer spent some time telling me how misunderstood he was and how nothing I could change would make a difference, and then he left, and Zach showed up and took me back to the present. Did the say-yes speech again. I told him to piss up a rope. He was all set to send me back when Cas—you—Castiel—popped in and yanked me out. And I called Sam, and we got back together."

The look on Cas's face was fascinating; he was clearly torn between being deeply skeptical and wanting to believe every word. "This didn't happen," he said. "Not just that you didn't come to the future, that could be in _my _future. But I never pulled you away from Zachariah in Kansas City. And you and Sam..."

"I know," Dean said, with a certain satisfaction. "That's what we're changing, Cas. Lucifer said 'No matter what details you change, we will always end up here.' Well, this ain't a detail. This is talking to my brother for the next five years, instead of not."

"Don't get me wrong, I'm OK with that," Sam said, a little dry. "But next time, I want the whole story, OK?"

"Sam," Dean started, but Sam said, "Secrets. They don't work. Pretty sure those were your exact words."

"Yeah, yeah, OK," Dean said. "I didn't keep it secret, it was just...he couldn't even run your face right, it was creepy. It was worse than that time with Meg, dude." Sam didn't look entirely convinced, but Dean didn't care; there was time for Sam to bitch him out later. "Anyway, none of that matters. We can change it. We're changing it already." He tried to catch Cas's eyes, and at first he couldn't, which was weird as hell; since when did Cas not make eye contact? But then he did, and Dean almost shuddered at the familiar look Cas gave him.

That look said _I did all of it for you_, and Dean still didn't know how to handle it, but it was better than the empty laughter, _Why not bang a few gongs before the lights go out_, and that was all Dean was going to worry about for now.


	3. The Hits Keep Coming

After a second, Dean said, "Look, do you need to get something to eat? There's a diner down the street." The practical question snapped Cas out of his stare, thank _God_, because Dean was trying really hard not to squirm.

"Yeah," Cas said, and ran his hands back through his hair. It didn't make it lie any flatter. "Yeah, but I wanna take a hot shower first. Been a while, you know?" In anyone else, Dean would've called his tone a desperate attempt to sound casual, and he wasn't sure what to do with it coming from Cas.

"Sure, yeah," he said. "You, um, need anything?"

Cas shook his head and scooted to the side of the bed. He sat there for a few seconds, his hands braced on the mattress at his sides, and stared some more, but at least it was at the floor instead of at Dean.

Sam, on his way to his laptop, said tentatively, "We can wash your clothes."

Cas looked up from contemplating his feet and gave Sam one of those wide, meaningless smiles. "That can wait till we get to Bobby's," he said. "I mean, I assume you're going to want to head there?" He glanced at Dean, and then away, and clapped his hands on his thighs as he stood; the gesture was bizarrely, jarringly human.

"Bobby's, yeah," Dean said, feeling like he was a half-step behind, and Cas nodded on his way to the bathroom.

"Great. Hey, do you have a package of razors in here?"

"Yeah. In the green—" Dean began, and Cas, one hand on the doorframe, threw him a look that was all indulgence.

"I know where you keep things, Dean," he said, and swung the door shut. Dean looked helplessly over at his brother, who was watching with an expression that suggested that something was becoming clear to him, and got a shrug.

"Hell," Dean muttered, and went to finish cleaning Sam's gun.

* * *

Cas stayed in the shower long enough that Dean actually started to worry; even the crappy motels he and Sam favored had continuous-flow water heaters, so it wasn't like Cas was sitting in there shivering, but Dean had to wonder what exactly he _was_ doing. It was close to half an hour before the water shut off.

When Cas emerged from the bathroom, he was clean-shaven; it made him look even thinner, if not much more respectable. He also looked like he wasn't wearing enough clothes for the weather, which was shaping up to be rainy and bone-achingly chilly. Dean couldn't persuade him to put on socks or heavier shoes; Cas just shrugged and said, "I don't get sick," and only accepted one of Dean's jackets because Dean told him he'd stand out too much without it. But by the time the dawn was well progressed (which was, at least, not as early as it would've been in summer) they were on their way to the diner.

Dean slid into the booth across from Sam before he thought about it, and ended up with Cas next to him. In and of itself that was OK, except Cas sat leaning back like he wanted to put his feet on the table and canted half-sideways, so close to Dean's side that Dean could feel his body heat. He gave Cas a skeptical look, and Cas grinned at him and didn't move.

The waitress was of the middle-aged, businesslike, not-impressed-by-your-charm-boy type, so Dean didn't try flirting with her. He ordered pancakes and bacon and coffee and rolled his eyes when Sam requested oatmeal—seriously, oatmeal, were they still twelve?

Then it was Cas's turn to order. He asked for oatmeal too (Sam covertly flipped Dean off, which Dean ignored). "That all?" the waitress asked, sounding bored.

"Pancakes," Cas said. "Blueberry, if you have them. Two orders of bacon, hash browns, anything you have in the way of fresh fruit, three scrambled eggs, coffee, and orange juice."

All three of them stared at him. The waitress's expression matched Sam's perfectly, and Dean had the feeling his own completed the set. "Please," Cas said sweetly. The waitress wrote on her order pad, said, "This might take a little bit," and headed for the kitchen, beaming disbelief into the air around her so hard Dean could almost see it.

He turned back to Cas and was opening his mouth when Sam said, "Hungry?"

"I was living in the Apocalypse," Cas said. He didn't sound even a little defensive, just matter-of-fact. "You know how long it's been since I've had bacon?"

"That's just a lot of food," Sam said, and Cas laughed, too loud in the otherwise-empty diner, though at least he'd lowered his voice to say "Apocalypse".

"I'm really hungry," he said. "Not enough to go around, and people who screw up get short rations. To be fair he does it to himself too."

"Who?" Sam asked, his forehead wrinkling in puzzled concern. Dean turned to look out the window, because he already knew the answer to that one.

"Dean," Cas said in a tone that suggested it was obvious. "It's pretty effective, all things considered."

"Shoulda punched that dick when I had the chance," Dean muttered to the parking lot.

There was a pause, then Sam said, "You can make yourself sick trying to eat too much." He was doing the Sincere Voice that Dean hated because he still had no damn defense against it, twenty five damn years after Sam learned to talk.

Cas sighed and actually reached across the table to pat Sam's hand. "It's fine," he said. "Last night's adventure notwithstanding, I do know my limits." Apparently Cas couldn't take the Sincere Voice either.

Sam didn't reply, and after a second Cas poked Dean in the shoulder and said, "When were you there?"

Dean blinked and turned back to look at Cas, whose expression was no more than mildly curious. "Uh, where?"

Cas rolled his eyes and said, "The future, Dean, don't play dumb. When was it?" Dean had no idea what to say; it must have shown on his face because Cas went on impatiently, "Come on, I need to know my expiration date if I'm gonna plan ahead. Be a shame to let my stash go to waste."

"But—no, Cas, you're here now. You're not going back."

"You can't guarantee that," Cas said, with a sudden total seriousness that made him Castiel again, just for a second. "We have no idea how I got here, so we _have to _assume I'm going back." He smiled, a small and bitter thing that was still more real than any other smile Dean had ever seen on his face. "It's a nice vacation, but I can't count on it."

Dean stared at him, speechless, and after a second the smile broadened again and Cas's voice melted back into carefree sarcasm. "I mean, if I do stay...I'm not looking forward to living through the Apocalypse again, but at least here I'll have time for some more hot showers."

Dean had to work at it for a second, but finally he unclenched his jaw enough to say, "By the time I made it to the camp it was October second, the night of the second. We drove all night the third, got there right after dawn."

Cas chuckled and leaned his head back into the brown vinyl of the seat. "Oh, man. Oh, that's...that's perfect."

"What day was it when you...left?" Sam asked. He looked worried, not that that was anything new. Sometimes Dean thought worried was Sam's default expression.

"The thirtieth," Cas said, still staring at the ceiling and smiling.

"Thirtieth of what?" Dean asked, though he was fairly sure he didn't want to know the answer, and Castiel rolled his head enough to meet Dean's eyes.

"September," he said.

_Son of a bitch_, Dean thought. The waitress showed up with coffee cups, setting them down with a series of porcelain clinks. She poured in pointed silence, watching Cas skeptically; he either didn't notice or pretended not to.

When she was gone again, Cas said, "Dean told me he had a lead on the Colt, but I thought it was just like all the other leads. Guess not."

"Oh, crap," Dean said, because it was only just occurring to him that Cas didn't _know_. He met Sam's eyes and saw the same unhappy realization in them.

"What?" Cas asked, looking back and forth between them. He sat up straight and pulled one of the coffee cups close, reaching past Dean for the sugar dispenser.

"Things...other things are different here," Dean said carefully. "We got a line on the Colt. Managed to get hold of it." Cas tensed up again, still close enough to Dean's side that Dean could feel it. "Did you, you and_ I,_ go to Carthage? With Death?"

"Yes," Cas said slowly. He was pouring sugar into his cup at a rate that was visibly raising the level of the liquid. Dean didn't comment; the guy deserved to have his coffee however he liked it, even if how he liked it was sweet enough to rot teeth. "Ellen and Joanna Beth went with us, but they...damn. Here too?"

"Yeah," Sam said. "They still—"

"They still died," Dean said. "Because I froze up when I heard the hounds." His hands wanted to curl into fists, so he grabbed his own cup, ignoring Sam's sharp look; Sam had tried to convince him it wasn't his fault, but Dean knew better. "But that's, Jesus, not the important part."

Sam said, "I distracted him. He was in the middle of the ritual to raise Death, and I went up and let him monologue at me so Dean could get to him."

"I couldn't afford to miss," Dean said quietly, staring into his coffee so he wouldn't have to look at Cas. "So I waited till I was close, real close. Bet he got powder burns, that close. And I shot him in the head."

Cas set the sugar dispenser down very carefully and wrapped his hands around the cheap white coffee cup. "How long did it take for him to get back up?" he asked, his voice devoid of inflection.

No one said anything for a few seconds. Dean could hear the cook clattering around in the kitchen. Finally, Sam swallowed and said, "Not long."

Cas drew in a breath and held it. Dean glanced at him. He had his eyes closed, and no other expression on his face. "So the Colt doesn't work," Cas said at last.

"No," Dean said, and didn't know where to go from there.


End file.
